Metal/Oxygen Battery with Multistage Oxygen Compression

ABSTRACT

A vehicular battery system includes an oxygen reservoir having a first outlet and a first inlet, a multistage compressor supported by the vehicle and having a second inlet and a second outlet, the second outlet operably connected to the first inlet, a cooling system operably connected to the multistage compressor and configured to provide a coolant to the multistage compressor to cool a compressed fluid within the multistage compressor, and a vehicular battery system stack including at least one negative electrode including a form of lithium, the vehicular battery system stack having a third inlet removably operably connected to the first outlet, and a third outlet operably connected to the second inlet.

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application No. 61/767,596, filed on Feb. 21, 2013, thedisclosure of which is incorporated herein by reference in its entirety.

FIELD

This invention relates to batteries and more particularly tometal/oxygen based batteries.

BACKGROUND

Rechargeable lithium-ion batteries are attractive energy storage systemsfor portable electronics and electric and hybrid-electric vehiclesbecause of their high specific energy compared to other electrochemicalenergy storage devices. As discussed more fully below, a typical Li-ioncell contains a negative electrode, a positive electrode, and aseparator region between the negative and positive electrodes. Bothelectrodes contain active materials that insert or react with lithiumreversibly. In some cases the negative electrode may include lithiummetal, which can be electrochemically dissolved and depositedreversibly. The separator contains an electrolyte with a lithium cation,and serves as a physical barrier between the electrodes such that noneof the electrodes are electronically connected within the cell.

Typically, during charging, there is generation of electrons at thepositive electrode and consumption of an equal amount of electrons atthe negative electrode, and these electrons are transferred via anexternal circuit. In the ideal charging of the cell, these electrons aregenerated at the positive electrode because there is extraction viaoxidation of lithium ions from the active material of the positiveelectrode, and the electrons are consumed at the negative electrodebecause there is reduction of lithium ions into the active material ofthe negative electrode. During discharging, the exact opposite reactionsoccur.

When high-specific-capacity negative electrodes such as a metal are usedin a battery, the maximum benefit of the capacity increase overconventional systems is realized when a high-capacity positive electrodeactive material is also used. For example, conventionallithium-intercalating oxides (e.g., LiCoO₂,LiNi_(0.8)Co_(0.15)Al_(0.05)O₂Li_(Li)Ni_(0.3)Co_(0.3)Mn_(0.3)O₂) aretypically limited to a theoretical capacity of ˜280 mAh/g (based on themass of the lithiated oxide) and a practical capacity of 180 to 250mAh/g, which is quite low compared to the specific capacity of lithiummetal, 3863 mAh/g. The highest theoretical capacity achievable for alithium-ion positive electrode is 1794 mAh/g (based on the mass of thelithiated material), for Li₂O. Other high-capacity materials includeBiF₃ (303 mAh/g, lithiated), FeF₃ (712 mAh/g, lithiated), Zn, Al, Si,Mg, Na, Fe, Ca, and others. In addition, other negative-electrodematerials, such as alloys of multiple metals and materials such asmetal-hydrides, also have a high specific energy when reacted withoxygen. Many of these couples also have a very high energy density

Unfortunately, all of these materials react with lithium at a lowervoltage compared to conventional oxide positive electrodes, hencelimiting the theoretical specific energy. Nonetheless, the theoreticalspecific energies are still very high (>800 Wh/kg, compared to a maximumof ˜500 Wh/kg for a cell with lithium negative and conventional oxidepositive electrodes, which may enable an electric vehicle to approach arange of 300 miles or more on a single charge.

FIG. 1 depicts a chart 10 showing the range achievable for a vehicleusing battery packs of different specific energies versus the weight ofthe battery pack. In the chart 10, the specific energies are for anentire cell, including cell packaging weight, assuming a 50% weightincrease for forming a battery pack from a particular set of cells. TheU.S. Department of Energy has established a weight limit of 200 kg for abattery pack that is located within a vehicle. Accordingly, only abattery pack with about 600 Wh/kg or more can achieve a range of 300miles.

Various lithium-based chemistries have been investigated for use invarious applications including in vehicles. FIG. 2 depicts a chart 20which identifies the specific energy and energy density of variouslithium-based chemistries. In the chart 20, only the weight of theactive materials, current collectors, binders, separator, and otherinert material of the battery cells are included. The packaging weight,such as tabs, the cell can, etc., are not included. As is evident fromthe chart 20, lithium/oxygen batteries, even allowing for packagingweight, are capable of providing a specific energy >600 Wh/kg and thushave the potential to enable driving ranges of electric vehicles of morethan 300 miles without recharging, at a similar cost to typical lithiumion batteries. While lithium/oxygen cells have been demonstrated incontrolled laboratory environments, a number of issues remain beforefull commercial introduction of a lithium/oxygen cell is viable asdiscussed further below.

A typical lithium/oxygen electrochemical cell 50 is depicted in FIG. 3.The cell 50 includes a negative electrode 52, a positive electrode 54, aporous separator 56, and a current collector 58. The negative electrode52 is typically metallic lithium. The positive electrode 54 includeselectrode particles such as particles 60 possibly coated in a catalystmaterial (such as Au or Pt) and suspended in a porous, electricallyconductive matrix 62. An electrolyte solution 64 containing a salt suchas LiPF₆ dissolved in an organic solvent such as dimethyl ether or CH₃CNpermeates both the porous separator 56 and the positive electrode 54.The LiPF₆ provides the electrolyte with an adequate conductivity whichreduces the internal electrical resistance of the cell 50 to allow ahigh power.

A portion of the positive electrode 52 is enclosed by a barrier 66. Thebarrier 66 in FIG. 3 is configured to allow oxygen from an externalsource 68 to enter the positive electrode 54 while filtering undesiredcomponents such as gases and fluids. The wetting properties of thepositive electrode 54 prevent the electrolyte 64 from leaking out of thepositive electrode 54. Alternatively, the removal of contaminants froman external source of oxygen, and the retention of cell components suchas volatile electrolyte, may be carried out separately from theindividual cells. Oxygen from the external source 68 enters the positiveelectrode 54 through the barrier 66 while the cell 50 discharges andoxygen exits the positive electrode 54 through the barrier 66 as thecell 50 is charged. In operation, as the cell 50 discharges, oxygen andlithium ions are believed to combine to form a discharge product Li₂O₂or Li₂O in accordance with the following relationship:

Li ↔ Li⁺ + e⁻  (negative  electrode)${{\frac{1}{2}O_{2}} + {2{Li}^{+}} + {2e^{-}}}\underset{catalyst}{\leftrightarrow}{{Li}_{2}O\mspace{14mu} \left( {{positive}\mspace{14mu} {electrode}} \right)}$${O_{2} + {2{Li}^{+}} + {2e^{-}}}\underset{catalyst}{\leftrightarrow}{{Li}_{2}O_{2}\mspace{14mu} \left( {{positive}\mspace{14mu} {electrode}} \right)}$

The positive electrode 54 in a typical cell 50 is a lightweight,electrically conductive material which has a porosity of greater than80% to allow the formation and deposition/storage of Li₂O₂ in thecathode volume. The ability to deposit the Li₂O₂ directly determines themaximum capacity of the cell. In order to realize a battery system witha specific energy of 600 Wh/kg or greater, a plate with a thickness of100 μm must have a capacity of about 20 mAh/cm².

Materials which provide the needed porosity include carbon black,graphite, carbon fibers, carbon nanotubes, and other non-carbonmaterials. There is evidence that each of these carbon structuresundergo an oxidation process during charging of the cell, due at leastin part to the harsh environment in the cell (pure oxygen, superoxideand peroxide ions, formation of solid lithium peroxide on the cathodesurface, and electrochemical oxidation potentials of >3V (vs. Li/Li⁺)).

While there is a clear benefit to couples that include oxygen as apositive electrode and metals, alloys of metals, or other materials as anegative electrode, none of these couples has seen commercialdemonstration thus far because of various challenges. A number ofinvestigations into the problems associated with Li-oxygen batterieshave been conducted as reported, for example, by Beattie, S., D.Manolescu, and S. Blair, “High-Capacity Lithium-Air Cathodes,” Journalof the Electrochemical Society, 2009. 156: p. A44, Kumar, B., et al., “ASolid-State, Rechargeable, Long Cycle Life Lithium-Air Battery, ”Journal of the Electrochemical Society, 2010. 157: p. A50, Read, J.,“Characterization of the lithium/oxygen organic electrolyte battery,”Journal of the Electrochemical Society, 2002. 149: p. A1190, Read, J.,et al., “Oxygen transport properties of organic electrolytes andperformance of lithium/oxygen battery,” Journal of the ElectrochemicalSociety, 2003. 150: p. A1351, Yang, X and Y. Xia, “The effect of oxygenpressures on the electrochemical profile of lithium/oxygen battery,”Journal of Solid State Electrochemistry: p. 1-6, and Ogasawara, T., etal., “Rechargeable Li₂O₂ Electrode for Lithium Batteries,” Journal ofthe American Chemical Society, 2006. 128(4): p. 1390-1393.

While some issues have been investigated, several challenges remain tobe addressed for lithium-oxygen batteries. These challenges includelimiting dendrite formation at the lithium metal surface, protecting thelithium metal (and possibly other materials) from moisture and otherpotentially harmful components of air (if the oxygen is obtained fromthe air), designing a system that achieves acceptable specific energyand specific power levels, reducing the hysteresis between the chargeand discharge voltages (which limits the round-trip energy efficiency),and improving the number of cycles over which the system can be cycledreversibly.

The limit of round trip efficiency occurs due to an apparent voltagehysteresis as depicted in FIG. 4. In FIG. 4, the discharge voltage 70(approximately 2.5 to 3 V vs. Li/Li⁺) is much lower than the chargevoltage 72 (approximately 4 to 4.5 V vs. Li/Li^(|)). The equilibriumvoltage 74 (or open-circuit potential) of the lithium/oxygen system isapproximately 3 V. Hence, the voltage hysteresis is not only large, butalso very asymmetric.

The large over-potential during charge may be due to a number of causes.For example, reaction between the Li₂O₂ and the conducting matrix 62 mayform an insulating film between the two materials. Additionally, theremay be poor contact between the solid discharge products Li₂O₂ or Li₂Oand the electronically conducting matrix 62 of the positive electrode54. Poor contact may result from oxidation of the discharge productdirectly adjacent to the conducting matrix 62 during charge, leaving agap between the solid discharge product and the matrix 52.

Another mechanism resulting in poor contact between the solid dischargeproduct and the matrix 62 is complete disconnection of the soliddischarge product from the conducting matrix 62. Complete disconnectionof the solid discharge product from the conducting matrix 62 may resultfrom fracturing, flaking, or movement of solid discharge productparticles due to mechanical stresses that are generated duringcharge/discharge of the cell. Complete disconnection may contribute tothe capacity decay observed for most lithium/oxygen cells. By way ofexample, FIG. 5 depicts the discharge capacity of a typical Li/oxygencell over a period of charge/discharge cycles.

Other physical processes which cause voltage drops within anelectrochemical cell, and thereby lower energy efficiency and poweroutput, include mass-transfer limitations at high current densities. Thetransport properties of aqueous electrolytes are typically better thannonaqueous electrolytes, but in each case mass-transport effects canlimit the thickness of the various regions within the cell, includingthe cathode. Reactions among O₂ and other metals may also be carried outin various media.

In systems using oxygen as a reactant, the oxygen may either be carriedon board the system or obtained from the atmosphere. There are bothadvantages and disadvantages to operating a battery that reacts gaseousoxygen in a closed format by use of a tank or other enclosure for theoxygen. One advantage is that if the reaction chemistry is sensitive toany of the other components of air (e.g., H₂O, CO₂), only pure oxygencan be added to the enclosure so that such contaminants are not present.Other advantages are that the use of an enclosure can allow for theoperation at a high partial pressure of oxygen at the site of thereaction (for uncompressed atmospheric air the pressure of oxygen isonly 0.21 bar), can prevent any volatile species from the leaving thesystem (i.e., prevent “dry out”), and other advantages. Thedisadvantages include the need to carry the oxygen at all times,increasing the system mass and volume, potential safety issuesassociated with high-pressure oxygen, and others.

In order to realize the advantages that come with the use of a closedsystem in a vehicle it is necessary to compress the oxygen so that theoxygen volume is not too large on board the vehicle. In particular, apressure in the fully charged state of greater than 100 bar, such as 350bar (about 5000 psi), is desirable.

What is therefore needed is an economic, efficient, and compact methodto compress and store the oxygen produced during the charge of a batterysystem that consumes oxygen on discharge

SUMMARY

In one embodiment of the disclosure, a vehicular battery system includesan oxygen reservoir having a first outlet and a first inlet, amultistage compressor supported by the vehicle and having a second inletand a second outlet, the second outlet operably connected to the firstinlet, a cooling system operably connected to the multistage compressorand configured to provide a coolant to the multistage compressor to coola compressed fluid within the multistage compressor, and a vehicularbattery system stack including at least one negative electrode includinga form of lithium, the vehicular battery system stack having a thirdinlet removably operably connected to the first outlet, and a thirdoutlet operably connected to the second inlet.

In another embodiment, a method of operating a vehicular battery systemincludes removably coupling a vehicular battery system stack includingat least one positive electrode including a form of lithium to an oxygenreservoir and to a multistage compressor supported by the vehicle,discharging the vehicular battery system stack, transferring oxygenformed by discharging the vehicular battery system stack to themultistage compressor, compressing the transferred oxygen in a firstcompression stage of the multistage compressor, compressing thecompressed oxygen from the first compression stage in a secondcompression stage of the multistage compressor, providing coolant to themultistage compressor, and transferring the compressed oxygen from thesecond compression stage to the oxygen reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described features and advantages, as well as others, shouldbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and the accompanyingfigures in which:

FIG. 1 depicts a plot showing the relationship between battery weightand vehicular range for various specific energies;

FIG. 2 depicts a chart of the specific energy and energy density ofvarious lithium-based cells;

FIG. 3 depicts a prior art lithium-oxygen (Li/oxygen) cell including twoelectrodes, a separator, and an electrolyte;

FIG. 4 depicts a discharge and charge curve for a typical Li/oxygenelectrochemical cell;

FIG. 5 depicts a plot showing decay of the discharge capacity for atypical Li/oxygen electrochemical cell over a number of cycles;

FIG. 6 depicts a schematic view of a vehicle with an adiabaticcompressor operably connected to a reservoir configured to exchangeoxygen with a positive electrode for a reversible reaction with lithium;

FIG. 7 depicts a chart showing the mass and volume requirements for acarbon fiber O₂ storage tank;

FIG. 8 depicts charts showing the practical system energy and energydensity of a system including a carbon fiber tank for a 165 kWh pack,350 bar tank at ST with L/D of 3, 100 μm electrode for Li₂O₂ & LiMO₂,300 μm electrode for LiOH.H₂O, 20% excess Li, cell sandwich is 80% ofstack mass and 70% of stack volume, LiMO₂ capacity is 0.275 Ah/g, Eff.Li₂O₂: 90%, Eff. LiOH.H₂O: 90%, Eff. Li/LiMO₂: 95%;

FIG. 9 depicts a chart showing the increase in temperature when a gas isadiabatically compressed starting from a pressure of 1 bar and atemperature of 298.15 K with constant gas properties (i.e., gamma)assumed;

FIG. 10 depicts a chart showing compression work for an ideal gas(diatomic and constant properties are assumed for adiabatic) as afunction of pressure with the initial pressure at one bar; and

FIG. 11 depicts a process for how the temperature of the finalcompressed gas or of the gas at an intermediate stage is used by thebattery control system to change the flow rate of the cooling fluid toensure the correct final temperature is reached.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the disclosure is therebyintended. It is further understood that this disclosure includes anyalterations and modifications to the illustrated embodiments andincludes further applications of the principles of the disclosure aswould normally occur to one skilled in the art to which this disclosurepertains.

A schematic of vehicle 100 is shown in FIG. 6. The vehicle 100 includesa vehicular battery system stack 102 and an oxygen reservoir 104. Apressure regulator 106 governs provision of oxygen to the battery systemstack 102 during discharge while a multi-stage oxygen compressor 108 isused to return oxygen to the oxygen reservoir 104 during chargingoperations.

The battery system stack 102 includes one or more negative electrodes(not shown) separated from one or more positive electrodes (not shown)byone or more porous separators (not shown). The negative electrode (notshown) may be formed from lithium metal or a lithium-insertion compound(e.g., graphite, silicon, tin, LiAl, LiMg, Li₄Ti₅O₁₂), although Li metalaffords the highest specific energy on a cell level compared to othercandidate negative electrodes. Other metals may also be used to form thenegative electrode, such as Zn, Mg, Na, Fe, Al, Ca, Si, and others.

The positive electrode (not shown) in one embodiment includes a currentcollector (not shown)and electrode particles (not shown), optionallycovered in a catalyst material, suspended in a porous matrix (notshown). The porous matrix (not shown)is an electrically conductivematrix formed from a conductive material such as conductive carbon or anickel foam, although various alternative matrix structures andmaterials may be used. The separator (not shown) prevents the negativeelectrode (not shown)from electrically connecting with the positiveelectrode (not shown).

The vehicular battery system stack 102 includes an electrolyte solution(not shown) present in the positive electrode (not shown) and in someembodiments in the separator (not shown). In some embodiments, theelectrolyte solution includes a salt, LiPF₆ (lithiumhexafluorophosphate), dissolved in an organic solvent mixture. Theorganic solvent mixture may be any desired solvent. In certainembodiments, the solvent may be dimethyl ether (DME), acetonitrile(MeCN), ethylene carbonate, or diethyl carbonate.

In the case in which the metal is Li, the vehicular battery system stack102 discharges with lithium metal in the negative electrode ionizinginto a Li^(|) ion with a free electron e⁻. Li⁺ ions travel through theseparator toward the positive electrode. Oxygen is supplied from theoxygen storage tank 104 through the pressure regulator. Free electronse⁻ flow into the positive electrode (not shown).

The oxygen atoms and Li⁺ ions within the positive electrode form adischarge product inside the positive electrode, aided by the optionalcatalyst material on the electrode particles. As seen in the followingequations, during the discharge process metallic lithium is ionized,combining with oxygen and free electrons to form Li₂O₂ or Li₂O dischargeproduct that may coat the surfaces of the carbon particles.

LiLi⁺ + e⁻  (negative  electrode)${\frac{1}{2}O_{2}} + {2{Li}^{+}} + {2{e^{-}\underset{catalyst}{}{Li}_{2}}O\mspace{14mu} \left( {{positive}\mspace{14mu} {electrode}} \right)}$$O_{2} + {2{Li}^{+}} + {2{e^{-}\underset{catalyst}{}{Li}_{2}}O_{2}\mspace{14mu} \left( {{positive}\mspace{14mu} {electrode}} \right)}$

The vehicular battery system stack 102 does not use air as an externalsource for oxygen. External sources, meaning sources which are notcarried by the vehicle such as the atmosphere, include undesired gasesand contaminants. Thus, while the oxygen that reacts electrochemicallywith the metal in a metal/oxygen battery may initially come from theair, the presence of CO₂ and H₂O in air make it an unsuitable source forsome of the media in which the metal/oxygen reactions are carried outand for some of the products that form. For example, in the reaction ofLi with oxygen in which Li₂O₂ is formed, H₂O and CO₂ can react with theLi₂O₂ to form LiOH and/or Li₂CO₃, which can deleteriously affect theperformance and rechargeability of the battery. As another example, in abasic medium CO₂ can react and form carbonates that precipitate out ofsolution and cause electrode clogging.

In FIG. 6, all of the components are stored on board the vehicle 100.The volatile cell components are fully contained in the system. In someembodiments, the cell is configured to allow for periodic replacement ofone or more of the volatile components. For example, shutoff valves (notshown) and couplers (not shown) are provided in some embodiments toallow for isolation and removal of one or more of the tank 104, thevehicular battery stack 102, and the multistage compressor 108. Thisallows, for example, the easy replacement of failed or depletedcomponents such as battery stacks with depleted electrolyte.Additionally, in the event the compressor fails, oxygen generated duringdischarge may simply be vented to atmosphere and a replacement oxygentank inserted to allow for continued battery operation.

The mass and volume of the complete battery system (upper limit forsmall vehicle) should be <400 kg (>415 Wh/kg)—mass reference value, and<275 L (>600 Wh/L)—volume reference value. The mass of O₂ for 165 kWh is33.3 kg for Li₂O₂ and 14.5 kg for LiOH.H₂O. The flow rate of O₂ for 100kW at STP, 90% efficiency, stoich=1 is 4.4 L/s of O₂ for Li₂O₂ and 1.9L/S for LiOH.H₂O. The gas handling power requirement is ideally <5% ofthe discharge power. With a battery cost target of 100 $/kWh and the gashandling at 20% of battery system, the cost would be 3.00 $/StandardLiter Per Minute (SLPM) of air for Li₂O₂.

In the embodiment of FIG. 6, the oxygen storage reservoir 104 isspatially separated from the vehicular battery system stack 102 wherethe reactions take place, but in other embodiments the oxygen storage ismore closely integrated with the stack (for example, incorporated withinthe cells). In the embodiment of FIG. 6, the oxygen is stored in a tankor other enclosure that is spatially separated from the stack or cellswhere the reactions are carried out such that a minimal amount ofhigh-pressure housing is required for the vehicle 100. In oneembodiment, the storage reservoir 104 is a carbon fiber tank. Carbonfiber tanks with pressures of ˜350 and 700 bar have been explored forstoring H₂ for PEM fuel cells. For a 165 kWh pack, a carbon fiber tankat 350 bar would provide sufficient O₂ as indicated by FIGS. 7 and 8.

During discharge (in which oxygen is consumed), the pressure of theoxygen gas is reduced by passing it through the pressure regulator 106such that the pressure of the oxygen that reaches the stack is close toambient (i.e., less than about 5 bar). During discharge the compressor108 does not operate. During charge the compressor 108 is operated tocompress the oxygen that is being generated within the stack or cellswhere the reactions are taking place.

The compressor 108 in various embodiments is of a different type. In oneembodiment which is suitable and mature for a vehicle application inwhich it is desired to pressurize a gas to more than 100 bar in a unitwith a compact size, the compressor 108 is a multi-stage rotarycompressor. When embodied as a multi-stage rotary compressor, eachcompression step is nearly adiabatic because it involves the rapidaction of a piston to compress the gas. This type of compressor unit iswell known. For example, U.S. Pat. No. 6,089,830 which issued Jul. 18,2000, the entire contents of which are herein incorporated by reference,discloses a multistage rotary compressor. Commercial units of theappropriate size are widely available at a reasonable cost; they areused for a variety of applications that require air compression.

Because each stage of the compressor is nearly adiabatic, in addition toan increase in the pressure there is also an increase in thetemperature, as explained with reference to FIG. 9. FIG. 9 shows thetemperature at the end of a single adiabatic compression step startingat a pressure of 1 bar and a temperature of 298.15 K assuming constantgas properties. The figure shows that it is impractical to use a singlecompression step to achieve a pressure of, for example, 350 bar, becausethe output temperature would be far too high to inject into a tank ofstandard materials, which in turn is integrated in a vehicle that mayhave heat-sensitive components. In addition, the final pressure shown inFIG. 9 is for the temperature at the end of the compression step; thus,after cooling, the pressure will fall. It is important for thetemperature of the compressed gas released into the tank to be within acertain range so that it is compatible with the tank material, which indifferent embodiments is a metal such as aluminum or a polymer,depending on the type of tank.

In order to prevent the temperature from rising too high it is necessaryto cool the gas at the end of each adiabatic compression step. This isaccomplished using the radiator 110 shown in FIG. 6. The radiator 110 insome embodiments is the same radiator that is used to cool the batterysystem stack; in such embodiments the heat exchange loop also extendsinto the other components of the battery system such as the batterysystem stack 102 and battery system oxygen storage 104. Typically, fluidis passed through the oxygen compressor 108, removing heat from theoxygen gas after each compression step and bringing the temperaturetowards that of the radiator fluid. The fluid is passed through theradiator 110 where heat is exchanged with the atmosphere. The compressoris also insulated to prevent the exposure of other parts of the batterysystem or the vehicle 100 to high temperatures.

The cooling of the oxygen after each compression step allows the systemto operate closer to the isothermal compression work line shown in FIG.10. In particular, FIG. 10 shows the difference in the work required fora single-stage adiabatic compression (assuming a diatomic gas andconstant properties) compared to the compression work required forisothermal compression. As the figure shows, significantly more work isrequired for adiabatic compression than isothermal compression. For amulti-stage adiabatic compression process with cooling between stagesthe amount of work required is between the pure isothermal andsingle-stage adiabatic lines. Thus, the amount of work required for thecompression can be lowered compared to adiabatic compression by usingmultiple compression stages with cooling of the gas at the end of eachcompression.

The magnitude of the compression energy compared to the reaction energyalso depends on the negative electrode material with which oxygen isreacting. For example, if the oxygen is reacting with Li to form Li₂O₂on discharge, the reaction energy is 159 Wh/mole O₂. Thus, if thecharging process takes place with 85% efficiency, about 24 Wh/mole O₂would be required for cooling for the reaction, suggesting that theamount of cooling required for the compression should be smaller thanthat required for cooling the stack or cells.

In some embodiments, some or all of the oxygen generated during chargeis vented to atmosphere. For example, in situations where extremetemperature changes are experienced, the tank may approach anoverpressure condition during recharge, or the maximum pressurecapability of the compressor may be reached. Depending upon theparticular embodiment, one or more vents (not shown) may be positionedbetween the battery system stack 102 and the compressor 108, after oneor more compression stages in the compressor 108, or on the oxygenstorage reservoir 104. In some embodiments, one or more of the vents areautomatic vents, while in some embodiments one or more of the vents areunder control of the battery control system 112.

In some of these embodiments, a gas regeneration system is used toprovide supplemental oxygen during discharge. In other embodiments, areplacement oxygen tank is provided. The free energy of separating the 5highest-concentration species in air (N₂, O₂, H₂O, Ar, CO₂) is <0.5Wh/mol air, which is lower than the compression energy for 1 to 350 bar(˜3.50 Wh/mol). Most of the free energy is associated with separating O₂and N₂, which in some embodiments is not done. Consequently, less than 2kW are required theoretically for this separation for a 100 kW dischargeforming Li₂O₂.

In the embodiment of FIG. 6, all processes associated with the operationof the battery system are controlled by a battery control system 112.The battery control system 112 controls the flow rate of the fluid thatis passed through the radiator 110 and the oxygen compressor 108 andpossibly other components on the vehicle 100. The battery control system112 includes a memory (not shown) in which program instructions arestored and a processor (not shown) which executes the programinstructions to control the temperature of the oxygen which iscompressed into the storage system 104. The processor is operativelyconnected to temperature sensors (not shown) in the battery system stack102, the oxygen storage 104, the radiator 110, and at various stages inthe compressor 108 in order to more precisely control the system. Insome embodiments, more or fewer temperature sensors are included. Aschematic that shows how the temperatures are used by the batterycontrol system 112 is shown in FIG. 11.

In FIG. 11, the processor obtains a signal indicative of the temperatureat the output of the compressor 108 and controls the flow rate of fluidbased upon the obtained temperature. In some embodiments, thetemperature of one or more intermediate stages of the compressor 108 isobtained, and cooling flow throw the particular stages is modified basedupon the temperature. In some embodiments, the temperature of thecooling fluid is obtained, and used to determine or control the flowrate of the cooling fluid.

The battery system stack 102 thus makes use of oxygen (which may be pureor contain additional components) stored within a battery cell orexternal to a cell in a tank or other volume. The oxygen reactselectrochemically with the metal (which may include Li, Zn, Mg, Na, Fe,Al, Ca, Si, and others) to produce energy on discharge, and on chargethe metal is regenerated and oxygen gas (and perhaps other species, suchas H₂O) are evolved.

Beneficially, the battery system in the vehicle 100 is thus a completelyclosed system and species present in ambient air (e.g., H₂O, CO₂, andothers) that may be detrimental to the cell operation are excluded. Thebattery system provides electrochemical compression of oxygen on charge,and the use of compressed oxygen on discharge, to reduce energy lossesassociated with mechanical oxygen compression (which is typicallycarried out adiabatically, including in a multi-stage adiabatic process)and to reduce the cost and complexity of a mechanical compressor. Thecomponents of the battery system are configured to handle the pressureof the compressed oxygen, including flow fields, bipolar plates,electrodes, separators, and high-pressure oxygen lines.

The battery system in some embodiments includes high-pressure seals, anelectrode, gas-diffusion layer, and flow field design that providesufficient mechanical support to prevent pressure-induced fracture orbending (including with pressure cycling) that would be deleterious tocell performance and life, and a separator that is impervious to oxygen(even at high pressures, including up to 350 bar or above). The minimumpressure in some embodiments is chosen to eliminate delamination of cellcomponents from one another. The minimum pressure in some embodiments ischosen to reduce mass transfer limitations and thereby increase thelimiting current.

The above described system provides a number of advantages. For example,the use of a multi-stage compressor results in a vehicle with a batterysystem that is smaller and more economical, and with a higherefficiency, than other compression strategies.

Additionally, a higher oxygen pressure in the tank can be achieved ifthe compressor is properly cooled than if there is not a good coolingsolution. In addition the compression can be carried out moreefficiently if the oxygen can be adequately cooled between each stage.

Moreover, the vehicle can be charged using only a wall outlet if acompressor is integrated into the vehicle system itself rather thanstored externally from the vehicle.

Integration of the compressor on the vehicle allows for a completelyclosed gas handling system. If a compressor is stored separately fromthe vehicle a connection between the external compressor and the gashandling system on the vehicle may introduce contamination.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. Only the preferredembodiments have been presented and all changes, modifications andfurther applications that come within the spirit of the disclosure aredesired to be protected.

What is claimed is:
 1. A vehicular battery system comprising: an oxygenreservoir having a first outlet and a first inlet; a multistagecompressor supported by the vehicle and having a second inlet and asecond outlet, the second outlet operably connected to the first inlet;a cooling system operably connected to the multistage compressor andconfigured to provide a coolant to the multistage compressor to cool acompressed fluid within the multistage compressor; and a vehicularbattery system stack including at least one negative electrode includinga form of lithium, the vehicular battery system stack having a thirdinlet removably operably connected to the first outlet, and a thirdoutlet operably connected to the second inlet.
 2. The vehicular batterysystem of claim 1, wherein: the first inlet is removably operablyconnected to the second outlet.
 3. The vehicular battery system of claim2, further comprising: a vent operably connected to the vehicularbattery system.
 4. The vehicular battery system of claim 3, wherein thevent is positioned on the oxygen reservoir.
 5. The vehicular batterysystem of claim 3, wherein the vent is positioned on the multistagecompressor.
 6. The vehicular battery system of claim 1, wherein theoxygen reservoir is located within the vehicular battery system stack.7. The vehicular battery system of claim 1, wherein the oxygen reservoircomprises a carbon fiber tank spatially separated from the vehicularbattery system stack.
 8. The vehicular battery system of claim 1,further comprising: at least one sensor configured to generate a signalassociated with a temperature within the vehicular battery system; amemory; and a processor operably connected to the memory, the at leastone sensor, and the cooling system, the processor configured to executeprogram instructions stored within the memory to: obtain the signalgenerated by the at least one sensor, and control a flow of the coolantto the multistage compressor based upon the obtained signal.
 9. Thevehicular battery system of claim 8, wherein: the at least one sensorincludes a first sensor located at the second outlet; and the processoris further configured to execute the program instructions to obtain afirst signal generated by the first sensor, and control the flow of thecoolant to the multistage compressor based upon the obtained firstsignal.
 10. The vehicular battery system of claim 9, wherein: themultistage compressor includes a first compression stage and a secondcompression stage; a cooler is located between the first compressionstage and the second compression stage; the at least one sensor includesa second sensor located between the first compression stage and thesecond compression stage; and the processor is further configured toexecute the program instructions to obtain a second signal generated bythe second sensor, and control a flow of the coolant to the cooler basedupon the obtained second signal.
 11. A method of operating a vehicularbattery system comprising: removably coupling a first vehicular batterysystem stack including at least one positive electrode including a formof lithium to a first oxygen reservoir and to a multistage compressorsupported by the vehicle; discharging the first vehicular battery systemstack; transferring oxygen formed by discharging the first vehicularbattery system stack to the multistage compressor; compressing thetransferred oxygen in a first compression stage of the multistagecompressor; compressing the compressed oxygen from the first compressionstage in a second compression stage of the multistage compressor;providing coolant to the multistage compressor; and transferring thecompressed oxygen from the second compression stage to the first oxygenreservoir.
 12. The method of claim 11, further comprising: removablycoupling the first oxygen reservoir to the multistage compressor. 13.The method of claim 12, further comprising: decoupling the first oxygenreservoir from the multistage compressor and the first vehicular batterysystem stack; and removably coupling a second oxygen reservoir to themultistage compressor and the first vehicular battery system stack. 14.The method of claim 12, further comprising: venting oxygen generated bythe discharging of the first vehicular battery system stack.
 15. Themethod of claim 14, wherein venting oxygen comprises venting oxygen fromthe first oxygen reservoir.
 16. The method of claim 15, wherein ventingoxygen comprises venting oxygen from the multistage compressor.
 17. Themethod of claim 11, further comprising: providing supplemental oxygen tothe first vehicular battery system stack during a discharge of the firstvehicular battery system stack.
 18. The method of claim 11, furthercomprising: decoupling the first vehicular battery system stack from theoxygen reservoir and from the multistage compressor; and removablycoupling a second vehicular battery system stack including at least onepositive electrode including a form of lithium to the first oxygenreservoir and to the multistage compressor after decoupling the firstvehicular battery system stack.
 19. The method of claim 11, whereintransferring the compressed oxygen from the second compression stage tothe first oxygen reservoir comprises: transferring the compressed oxygenfrom the second compression stage to a carbon fiber tank spatiallyseparated from the first vehicular battery system stack.
 20. The methodof claim 11, further comprising: obtaining a signal generated by atleast one sensor associated with the vehicular battery system; andcontrolling a flow of the coolant to the multistage compressor with abattery control system based upon the obtained signal.